The present invention relates to an air-conditioner, an outdoor unit and a refrigeration unit using vapor compression refrigeration cycle, and in particularly, is preferable to those which enable a motor installed in a compressor to be driven by commercially available power source and, by which a wide range from low cost products till high cost products and commonness are progressed and kind expansion is facilitated.
As refrigerant compressors used in air conditioners, outdoor units and refrigeration units using vapor compression refrigeration cycle, a constant speed type compressor which is driven at a substantially constant speed, an inverter type compressor whose rotational speed is controlled have been used, and induction motors incorporating cage type conductors (windings) are often employed since they can be easily driven by an A.C. voltage of a commercial frequency and so forth. Further, it has been known that D.C. motors are often employed having a rotor formed by providing permanent magnets to a rotor core and a rotor formed by providing three-phase windings to a rotor core from a view point of high efficiency, as disclosed in JP-A-5-211796.
Further, as motors for industry, an embedded magnet synchronous motor which can be driven by a commercially available electric power has been proposed, in view of the need of energy saving, and it is disclosed in "The Super Economotor and its Applications" by Hirano et al, in Yasukawa Technical Bulletin Vol. 62 NO. 4, 1998, Series Volume No. 241.
In the above-mentioned prior art, the motor disclosed in JP-A-5-211796 is advantageous in view of its high efficiency, but in order to start the motor, it is indispensable to use an inverter, as a power source, whose frequency is variable. A power source circuit or the like becomes complicated, and in the case of a system having a refrigeration cycle, it becomes excessively complicated in a certain application, so as to be expensive.
Further, in order to use the embedded magnet synchronous motor of the above-mentioned prior art, in an air conditioner, an outdoor unit and a refrigeration unit in which refrigeration cycle is used, consideration should be taken to the discharge volume of refrigerant necessary for the refrigeration cycle and the efficiency of the refrigeration cycle also with respect to the rotational speed of the motor, for example, and further, it must avoid that the volume of a compression chamber of the compressor, the size of the overall compressor and the size of the outdoor unit in which the compressor is installed become large.
Further, upon starting the refrigeration cycle, if the differential pressure between the suction side and the discharge side of the compressor is large, there is a possiblity that the start becomes impossible even when the embedded magnet synchronous motor is used or its reliability becomes insufficient.
Further, if overload occurs during steady-state operation of the refrigeration cycle, that is, operation in synchronized condition, a rotor in the embedded magnet synchronous motor greatly stalls, or the temperature of the windings of the motor increases. In the worst case, the material of the windings would be deteriorated or the insulation of the windings would be broken, so that the reliability of the device would remarkably be deteriorated.
In addition, it is required to minimize the affection of the permanent magnets in the embedded magnet synchronous motor to deterioration of the refrigerant and lubrication oil circulating through the refrigeration cycle.